1. Field of the Invention
The present invention relates to a control apparatus of a vehicle. In particular, the invention relates to fuel injection control for a vehicle having, as its driving-force sources, an electric motor and an internal combustion engine having a first fuel injection mechanism for injecting fuel directly into a cylinder (in-cylinder injector) and a second fuel injection mechanism for injecting fuel into an intake manifold and/or an intake port (intake manifold injector).
2. Description of the Background Art
As one form of the internal combustion engine, a configuration of the internal combustion engine having an in-cylinder injector injecting fuel directly into a combustion chamber is proposed. In order to sufficiently atomize the fuel injected directly into the combustion chamber, it is necessary to set the pressure of the fuel injected from the in-cylinder injector to a higher pressure than the pressure of fuel injected from the intake manifold injector. To this end, generally a configuration is employed that uses a fuel-pressure boost system including an engine-driven high-pressure fuel pump which is driven according to rotations of the internal combustion engine, so as to increase the pressure of fuel of a low-pressure fuel supply system supplying fuel to be injected from the intake manifold injector. The resultant pressure-increased fuel is supplied as fuel to be injected from the in-cylinder injector.
Japanese Patent Laying-Open No. 2001-41088 (hereinafter Patent Document 1) and Japanese Patent Laying-Open No. 2001-50095 (hereinafter Patent Document 2) disclose that operation (particularly intermittent operation) of a spill valve functioning as a valve for adjusting the quantity of fuel whose pressure is increased by a high-pressure fuel pump causes an operating sound that could be felt unusual by a driver.
Further, a configuration is also proposed of an internal combustion engine having both of the above-described in-cylinder injector and intake manifold injector (see for example Japanese Patent Laying-Open No. 2002-364409, hereinafter Patent Document 3). Patent Document 3 discloses that such an internal combustion engine in a homogeneous-combustion operating mode injects fuel by both of the in-cylinder injector and the intake manifold injector for the purpose of preventing the in-cylinder injector from being kept at a high temperature.
Furthermore, in recent years, as a motor vehicle superior in fuel consumption and environmental performance, a hybrid vehicle has been developed having as its driving-force sources an internal combustion engine and an electric motor. In particular, the hybrid vehicle employs the configuration having a secondary battery and using electric power generated by the electric motor in a regenerative braking operating mode as well as the electric power generated by the electric generator driven by an engine output so as to charge the battery.
Thus, for the hybrid vehicle, whether or not the internal combustion engine is to be operated or stopped is determined in consideration of such factors as a required driving force for the whole vehicle as well as a request to charge battery. Generally, in a light-load running mode, the hybrid vehicle generates the vehicle's driving force by means of the electric motor only, for avoiding the use of the internal combustion engine in a low-efficient region. Even in such a case, however, if the battery charge quantity decreases, the internal combustion engine is started for charging the battery and operated in an idle mode. In this state, since the sound generated from the whole vehicle is low in volume, a driver is likely to sense the operating sound of the internal combustion engine. In particular, an internal combustion engine having the in-cylinder injector mounted thereon could generate the operating sound of the fuel-pressure boost system that is felt uncomfortable or unusual by the driver, as described in Patent Documents 1 and 2.
Accordingly, in the case where the internal combustion engine having the in-cylinder injector and the intake manifold injector like the one disclosed in Patent Document 3 is mounted on the hybrid vehicle, it is necessary to control the fuel injection while addressing the issue of deposit build-up due to an increase in temperature of the in-cylinder injector and giving consideration to the driver's sensibility to noise.